1. Field of the Invention
The present invention relates to a novel polymeric diacyl peroxide having a branched hydrocarbon group in the molecule, which is used as an initiator for free radical polymerization of vinyl monomer.
2. Description of the Prior Art
Heretofore, polymeric diacyl peroxides have been publicly known which are obtained by polycondensation of dicarboxylic acid chlorides and sodium peroxide. That is, Berichte, vol. 27, p. 1510 (1894) reports a polymeric diacyl peroxide obtained by polycondensation of phthalic chloride and sodium peroxide, J. Amer. Chem. Soc., vol. 68, p. 534 (1946) reports polymeric diacyl peroxide obtained by reacting oxalic chloride with sodium peroxide, and Chem. Abst, vol. 60, 5293d and 10892e (1964) reports a polymeric diacyl peroxide having the following formula: ##STR1## wherein n is 2-10 and x is 16-35 obtained by reacting aliphatic dicarboxylic acid chloride with sodium peroxide. Further, Japanese patent application laid-open No. 149,918/78 discloses a polymeric diacyl peroxide having an ester bond in the molecule obtained by reacting an acid chloride having an ester bond in the molecule with sodium peroxide.
It has been publicly known also that the above described polymeric diacyl peroxides are useful as initiators for free radical polymerization (hereinafter abbreviated as "polymerization initiator") of vinyl monomer. For example, Chem. Abst, vol. 67, 54445a (1967) reports that if the above polymeric peroxide is used as a polymerization initiator a polymer is obtained having a larger molecular weight which is about twice as much than that obtained by using benzoyl peroxide. Chem. Abst, vol. 84, 136120f (1976) reports that if the above polymeric peroxide is used as a polymerization initiator of vinyl acetate a polymer is obtained having a larger molecular weight and less branching as compared with a polymer obtained by using benzoyl peroxide. Journal of the Chemical Society of Japan vol. 69, p. 718 (1966) reports that if poly(phthaloyl peroxide) is used as a polymerization initiator a styrene-methylmethacrylate graft polymer is obtained.
As mentioned above, the publicly known polymeric diacyl peroxides are useful polymerization initiators. However, the publicly known polymeric diacyl peroxides not having an ester bond in the molecule have drawbacks that; (1) they are detonative compounds sensitive to impact and friction (refer to Chem. Abst, vol. 59, 7651 (1963)), and (2) they have low solubility in organic solvents and are completely or substantially insoluble in vinyl monomer, so that they can not be used as polymerization initiators industrially (refer to Journal of the Chemical Society of Japan vol. 69, p. 718 (1966) and Chem. Abst, vol. 64, 15989g (1968)). This feature has a close relation with catalyst efficiency. If a polymerization initiator of a low solubility is used for polymerization, catalyst efficiency thereof becomes low.
The aforementioned polymeric diacyl peroxide having an ester bond in the molecule has an advantage of improving the above described two drawbacks, however, it has the following shortcomings. Namely, the material acid chloride having an ester bond in the molecule is produced by a two-steps process under a dry air or nitrogen stream, so that its production requires a prolonged time and special devices and hence it is time consuming and expensive in cost and commercially disadvantageous.